SURFACE-ROUGHNESS OF MO FILMS PREPARED BY MAGNETRON SPUTTERING

The surface roughness of Mo films, prepared with different Ar gas pressures and r.f. powers in a magnetron-sputtering apparatus, was measured by means of the gas absorption technique, eg. the Brunauer-Emmett-Teller method. It was observed that the roughness was enhanced by an increase in gas pressure and a decrease in r.f. power level. Scanning electron microscopy observations showed the growth of columnar structure on the surface with a large surface roughness. The X-ray diffraction analysis showed that the crystallinity deteriorated on increase in the gas pressure. In order to explain the growth of columnar structure, the optical emission spectroscopy technique was applied to measure the spatial distribution of emitted Mo atoms. The intensity of emitted Mo atoms rapidly decreased on increase in the gas pressure in the vicinity of the substrate. This result suggests that the collision probability of an Mo atom with an Ar atom is enhanced and that the incident angle then becomes not normal to the substrate, e.g. relatively isotropic. The growth of the columnar structure is thus attributed to the shadowing effect associated with the film deposition process.